The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an active bolster with an inflatable bladder formed by plastic wall panels that are hot welded to form a hermetic seal wherein one wall is vented for a controlled release of inflation gas.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deployable air bag cushions made of various fabrics that emerge from behind various openings upon inflation, active bolsters use the interior trim surface (e.g., instrument panel dashboard, glove box, passenger door, or seat back) itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. U.S. Pat. No. 8,474,868, issued Jul. 2, 2013, also incorporated herein by reference, discloses a typical structure wherein an active bolster includes a front wall or trim panel that faces a vehicle occupant and is attached to a back wall or bladder member along a sealed periphery. One or both of the walls is deformable in order to provide an expandable, inflatable bladder. For example, the bladder member may have a pleated (i.e., accordion-like) region that straightens out during inflation.
The front and back walls of a typical bladder for an active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They are typically injection molded but can also be blow molded. When formed separately, the front and back walls must be hermetically joined around their periphery in order to form the inflatable bladder. The joint must be strong to resist separation that could result from high inflation pressures during inflation and that result when a passenger impacts the bolster. The peripheral seal is formed by hot welding, for example.
It is known that in order to optimize the dissipation of energy when an occupant contacts an air bag or an active bolster, inflation gas should be vented to allow a controlled collapse of the airbag that safely decelerates the impacting occupant. U.S. Pat. No. 8,720,943, issued May 13, 2014, which is incorporated herein by reference, discloses an active vent structure for providing a variable vent flow rate.
Various types of structures and locations on a pleated bladder member have been disclosed for venting inflation gas during inflation and during loading by an impacting passenger. Venting locations have been disclosed on the central, flat areas of the bladder wall, in the pleated baffle region of the bladder wall, and in welding towers that attach the bladder wall to a reaction surface, for example. It has been suggested that vents can be placed 1) in close proximity to local regions where the stresses of inflation forces may create a highest probability of weld failure, or 2) with a spatial distribution that adjusts the restraint forces provided at different regions of the bolster. Since it is desirable to locate the vent(s) close to the hot weld seam, the outermost pleat is often selected for the vent locations. With injection molding of the bladder member, the window openings for vents on the outermost pleat have been located at the top (i.e., peak) of the pleat since that facilitates the injection molding process and simplifies the molding tools. However, it has been discovered that in some circumstances the resulting gas flow has not provided the intended decrease in weld stress during the initial stages of inflation.